1211921011681 has 2 divisors, whose sum is σ = 1211921011682. Its totient is φ = 1211921011680.

The previous prime is 1211921011667. The next prime is 1211921011687. The reversal of 1211921011681 is 1861101291121.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 995495085025 + 216425926656 = 997745^2 + 465216^2 .

It is an emirp because it is prime and its reverse (1861101291121) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1211921011681 is a prime.

It is a super-3 number, since 3×1211921011681³ (a number of 37 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is not a weakly prime, because it can be changed into another prime (1211921011687) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 605960505840 + 605960505841.

It is an arithmetic number, because the mean of its divisors is an integer number (605960505841).

Almost surely, 2^{1211921011681} is an apocalyptic number.

It is an amenable number.

1211921011681 is a deficient number, since it is larger than the sum of its proper divisors (1).

1211921011681 is an equidigital number, since it uses as much as digits as its factorization.

1211921011681 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1728, while the sum is 34.

The spelling of 1211921011681 in words is "one trillion, two hundred eleven billion, nine hundred twenty-one million, eleven thousand, six hundred eighty-one".